Boonruang Chunsuvimol and Nantana Ronnakiat (2004 : abstract) studied /v/ is really a problem sound for Thai speakers. The main purpose of this research is to investigate stylistic variation of /v/ in the English of Thai speakers. Three styles are chosen in this study conversation (informal) reading text (formal), and minimal pairs very (formal). The data analysis shows that there is a significant difference between the use of syllable-initial and word /-fmal/, /v/. Most of syllable-initial /v/ occurs as /v/ in each style while the word /-fmal/, /v/ occurs most frequently as /f/, followed by /v/.
The results found that /v/ sound is really a problem sound for Thai speaker because /v/ sound have no in Thailand that it is a problem in pronunciation for Thai speakers.How ever pronouncing /v/ sound still necessary to reading in English consonant and if Thai speakers correct pronunciation in /v/ sound it is good for their.